Peugeot 206 starting

When starting the car in the morning or when it is cold, it runs very rough and cuts out if no accelerator applied but, as the car warms up, the roughness disappears and the car runs and idles without problem. The starting problem does not occur when car is warm. Initially, the car blew a white /(blue(?))smoke but this has lessened. When car is warm, this does not happen, although, on 3 earlier occasions,there was a big billow of smoke from the exhaust when driving. Although I feel I am using more petrol, I am not using extra water or oil. In fact, according to the dipstick (not the original), the engine oil is above full and remains there. I took the car to a garage who put it on their tester and they told me that the car's parameters were not indicating any problem. The problem however is slowly getting worse.